Frequent mouth ulcers and drowsiness may be caused by decreased immune function and psychological factors, as follows. 1. Decreased immune function: Decreased cellular immune function may cause mouth ulcers, and at the same time, symptoms such as drowsiness, fatigue, and low quality of sleep, dreamy and easy to wake up. 2. Psychological factors: the patient’s behavioral type, life events, work environment, etc. can cause psychological reactions, anxiety, stress, depression and other psychological factors and mouth ulcers have a certain relationship, and may have drowsiness symptoms. Frequent mouth ulcers and drowsiness may have other reasons, it is recommended to go to the hospital in time, clear causes for targeted treatment.